Conventional wind turbines used as wind power generators include a nacelle installed at the top of a tower and more than one blade. The nacelle is configured to be rotatable on the tower and a generator and the like is disposed thereinside. The blades are installed such that they are rockable in the pitch direction with respect to a rotor which is a main shaft attached to the nacelle. In the wind turbines, a yaw driving device is provided as a wind turbine driving device that drives the nacelle. The yaw driving device drives the nacelle to be rotated relative to the tower so that the nacelle can be turned in accordance with a wind direction. In the wind turbines, a pitch driving device is further provided as a wind turbine driving device that drives the blades. The pitch driving device drives and turns axes of the blades relative to the rotor in the nacelle in order to change pitch angles of the blades.
A wind turbine driving device used as the above-mentioned yaw driving device or the pitch driving device includes an electric motor, a speed reducer, and a pinion. For instance, a geared motor disclosed in Patent Literature 1 may be used as the wind turbine driving device. The speed reducer is coupled to an output shaft of the electric motor in the wind turbine driving device. The pinion is disposed in an output portion coupled to the speed reducer and configured to be meshed with a ring gear that is disposed in the wind turbine. Moreover, a braking mechanism for stopping the output shaft of the electric motor is provided in the wind turbine driving device.